The invention relates to a method for producing a component from stacked plates soldered to one another, such as a micro-heat exchanger.
By way of example, micro-heat exchangers are suitable for use in air conditioning systems. Moreover, micro-heat exchangers can be used in cooling electronic components, for instance in power electronics.
For reducing the mass and/or volume, particularly in vehicles, there is a need for compact production of the heat exchanger. For that purpose, in some embodiments, plates in which conduits are made are put together to form complete structural parts. The conduit structures can be produced by applying material, or by removing material. In the removal type of production, suitable conduits are milled out of a material, or etched, or for instance created by laser machining. It is thus possible to produce conduit structures in which a fluid can flow. In the material-applying type of production, structures are constructed on a substrate, for instance by an electroplating step. Joining together individual plates is typically done by soldering methods. Applying terminals cannot always be taken care of in a single production operation.
From German Patent 198 01 374 C1, a method for soldering metal, microstructured sheets is disclosed. In this method, a stack is created from the sheets and from electrical terminals located between each two adjacent sheets, and with the application of pressure in a vacuum or in an inert gas atmosphere, the stack is subjected to a solder diffusion process. This is done in a suitably hermetically sealed furnace. In this operation, subjecting a stack of microstructured sheets to pressure, in particular, is comparatively complicated. This is because suitable pressing tools are heated to the soldering temperature along with the structural parts to be produced and must therefore be capable of withstanding these temperatures.
The object of the invention is to simplify the production of components of the type defined at the outset.
The invention is based on a method for producing a component out of stacked plates soldered to one another, into at least some of which recesses are made, in which method, at least one solder layer is provided between the plates for a solder diffusion process. The solder diffusion process is favorably performed in a vacuum or in an inert gas atmosphere. The nucleus of the invention is that the plates, with the at least one solder layer between them, are stacked on one another in the later disposition of the structural part, and are also compressed, preferably in the cold state, before the solder diffusion process. The invention makes use of the recognition here that a sufficiently good connection of the individual plates in the solder diffusion process can already be attained if compressing of the plates is done before the actual solder diffusion operation, which makes a comparatively strong compressing of the plates in the solder diffusion process at temperature unnecessary. Thus complicated pressing tools, which would otherwise have to withstand the high soldering temperatures, can be dispensed with.
In an especially preferred feature of the invention, the stack of plates and solder layers is made heavier by a weight, such as a steel block, during the solder diffusion operation. Because of the precompression, it is often not possible, in the solder diffusion operation itself, to dispense entirely with pressing the plates together. However, a comparatively low pressing force is already sufficient and can be furnished by a weight placed on them that would normally not suffice to apply a requisite pressure force without precompression.
In a further, especially preferred feature of the invention, the stack of plates and solder layers, for the solder diffusion process, is placed in a receptacle. By this provision, secure positioning of the stack of plates in the soldering operation is assured. Preferably, the bearing face of the receptacle is coated in such a way that connecting the surface of the receptacle to the stack of plates to be soldered is averted.
To further improve the separation between the receptacle and the stack of plates to be soldered, it is moreover proposed that a high-temperature-proof insulating material is placed between the receptacle and the stack of plates.
To prevent an already-soldered stack of plates from being damaged when terminals, for example, are attached directly in a later soldering process, it is moreover proposed that later soldering process is performed at a lower temperature than the preceding soldering process.
For rational production and to assure a secure soldered connection, it is moreover proposed that before the compacting and soldering, a solder layer, such as a bronze layer, is applied to the plates by an electrolytic method. For a later soldering process under negative-pressure conditions, care must be taken to assure that the coating have the least possible gloss, to prevent outgassing. If the coating tends to oxidize upon contact with air, then oxidation products created in the process are preferably removed before the soldering operation, for example by immersion in a suitable solution.
In another preferred feature of the invention, the plates are provided with recesses by means of a photolithographic structuring process with a later etching process, in order to make flow conduits, for instance.